Digital watermarking is a process for modifying media content to embed a machine-readable code into the data content. The data may be modified such that the embedded code is imperceptible or nearly imperceptible to the user, yet may be detected through an automated detection process. Most commonly, digital watermarking is applied to media such as images, audio signals, and video signals. However, it may also be applied to other types of data, including documents (e.g., through line, word or character shifting), software, multi-dimensional graphics models, and surface textures of objects.
Digital watermarking systems have two primary components: an encoder that embeds the watermark in the media content, and a decoder that detects and reads the embedded watermark. The encoder embeds a watermark by altering data samples of the media content. The reading component analyzes content to detect whether a watermark is present. In applications where the watermark encodes information, the reader extracts this information from the detected watermark.
The invention provides a system and related methods for encoding and decoding watermarks from media signals, including image and audio signals, using multiple carriers. A multi-carrier watermark system includes a watermark embedder and compatible decoder. The embedder encodes auxiliary information, such as a binary message, into the host media signal by modulating message signals with two or more corresponding carrier signals to form a watermark signal and embeds this signal into the host signal. A compatible watermark decoder uses the carrier signals to demodulate the message signals from the watermarked signal.
Further features of the invention will become apparent with reference to the following detailed description and accompanying drawings.